1. Field of the Invention
This invention relates to pivotally mounted caps of the type used for closing the atmospheric opening of an exhaust pipe at a time when exhaust gas is not being vented therethrough, and more particularly, to a dynamically balanced closure cap for an exhaust pipe, which cap is geometrically so configured, and has its mass so distributed, that it functions effectively and resists counteractive wind and gravity forces.
2. Brief Description of the Prior Art
Efforts to provide better dynamic balancing in caps for diesel engine exhaust pipes have taken various forms. Thus, in Stade et al U.S. Pat. No. 2,983,216, a rain cap for an engine exhaust pipe is provided, and this cap is of the gravity actuated-type in which the cover member is adapted to fit over the open end of the stack or exhaust pipe, and carries a counterbalancing section or portion which is pivotally supported in a way, and at a location, such that the cap tends, by reason of the shift of the center of gravity, to reseat or close when the exhaust gases are not acting on the cap to open it.
This cap is susceptible, however, to opening under wind pressure, or the pressure of air developed as the tractor upon which the cap is mounted is carried over the road on a transport vehicle if the cap is faced in an improper direction. In the full closed position, the cap extends horizontally across the upper end of the exhaust pipe, and it is therefore necessary for the cap to open through almost 90.degree. in order for it to achieve a fully open position. This requires the exertion of a greater opening force from the exhaust gases which are being vented through the exhaust pipe, and can result in an undesirably high level of back pressure being exerted on the exhaust gases attempting to pass through the exhaust pipe. Also, in this situation where the cap extends horizontally across the squared off upper end of an exhaust pipe of this type, the cap has further to fall to its closure position under the influence of gravity when the gas pressure is relieved. This results in a very undesirable loud banging noise as the cap seats in its closed position against the top of the exhaust pipe.
Bauerschmidt U.S. Pat. No. 3,523,499 discloses a weather cap construction for an exhaust pipe. The weather cap is held on the exhaust pipe by a collar which is closed about the exhaust pipe by a suitable clamping bolt. This construction has the advantage of allowing the collar to be varied some in size so that it can be fitted tightly about exhaust pipes of different sizes. In the Bauerschmidt cap, the pivoted closure element is supported for pivotation about a pivotal axis which is displaced laterally from the vertical axis of the exhaust pipe by a substantial distance, and when the cap is in its elevated, fully opened position, it exerts essentially no back pressure on the gases passing from the exhaust pipe. It must, however, open through an angle which is almost 90.degree., and therefore in the initial phase of the opening arc, an undesirable amount of back pressure may be exerted on the exhaust gases. A positive stop is provided to limit how far the crank upon which the closed cap is carried will open in its full open position, and this positive stop is in a position such that the center of gravity still remains inside the pivotal axis. The crank arm will therefore fall rapidly, under the influence of gravity, to a closed position, once the exhaust gases cease to be vented through the exhaust pipe.
In De Penning U.S. Pat. No. 3,363,537, a tractor exhaust pipe cover is illustrated and described. The cover depicted includes a cap which pivots into, and away from, a horizontal plane representing the position of closure of the cap. The cap carries reflector devices in the form of a pair of platelike reflectors mounted on the opposite side of the pivotal axis of the cap structure from the cap plate proper. These reflectors afford some weight which assists the cap in opening in response to the force exerted by the upwardly moving exhaust gases.
Other types of exhaust cap structures are those which are depicted and described in Taylor U.S. Pat. No. 2,494,016; Burger U.S. Pat. No. 3,788,072 and Lukes U.S. Pat. No. 2,508,615.